This invention relates to the use of shrink tube and, more particularly, to a configuration of the shrink tube that is readily used to enclose bodies.
Shape-recovering material, sometimes also called heat-shrinkable or heat-recoverable material, is widely used in marking and packaging applications. A working definition used herein is that the shape-recovering material is a polymer having materials properties described by a contracted state and an expanded state which contracts toward the contracted state upon heating.
When the shape-recovering material is provided in shrink-tube form, it is typically structured to contract to or toward a specified size in the contracted state. In its initial manufacturing, the shape-recovering material is typically extruded in a particular shape and size, expanded to the expanded state, and thereafter cooled so that the expanded state is retained. When it is to be used in service, the expanded and cooled material is placed overlying a body to be enclosed, and then again heated so that it contracts back toward the contracted state, thereby enclosing the body in a polymeric covering.
The shape-recovering material is sometimes used to enclose an electrical cable having a connector at each end thereof. In this application, the shape-recovering hollow tube of about the same length as the electrical cable is slipped over the electrical cable. The individual wires of the electrical cable are electrically connected to the terminals of the connectors. In order to have room to separate the individual wires and perform the electrical connections, the hollow tube is pushed back away from the connector to shorten its length in an accordion fashion. After the electrical connections are made, the hollow tube is allowed to relax back to its full length, and then it is heated to contract it to the contracted state.
While operable and widely used, this approach is inconvenient because it is difficult to shorten the hollow tube against the constraint of the enclosed electrical cable and because it is necessary to hold the hollow tube in the shortened configuration while the electrical connections are made. This holding in the shortened configuration may be accomplished manually or with a tool such as a clamp, but either approach interferes with the required electrical connection procedure. Also, for practical purposes the tubing is normally cut longer than the anticipated final assembled length, making the assembly even more difficult.
There is a need for an improved approach to the use of shape-recovering hollow tubes for enclosing bodies such as electrical cable. The present invention fulfills this need, and further provides related advantages.
The present invention provides a hollow shrink tube that is well suited for easy placement over a body such as an electrical cable. It is in a shortened telescoped form that is shorter than the body, so that the ends of the body are readily accessible. Cable connectors may be easily attached to the ends of the electrical cable, for example. The hollow shrink tube may then be telescoped back to its full length for subsequent contraction around the body. The shortened hollow shrink tube is readily prepared and avoids the need for awkward procedures to otherwise hold the shrink tube in the shortened form while attaching cable connectors. The shortened form of the tube is convenient for shipping and storage, such as in repair kits.
In accordance with the invention, a method for preparing an article includes preparing a shrinkable hollow tube. The hollow tube is made of a shape-recovering polymeric material having materials properties described by a fully contracted state, an expanded state which contracts toward the fully contracted state upon heating, and a partially contracted state resulting from a partial contracting from the expanded state toward the fully contracted state. The step of preparing is accomplished by providing a hollow tube in the expanded state, partially contracting a portion of the hollow tube, resulting in a first length of the hollow tube in the expanded state and a second length of the hollow tube in the partially contracted state, and folding the first length over the second length so that the first length radially overlies the second length. The folding step includes folding the first length once, twice, or more times over the second length to shorten the hollow tube. The total length of the hollow tube is thereby telescoped to a shorter length.
In use, a body such as an electrical cable is inserted into the hollow tube. The insertion is normally accomplished after the step of preparing, but it may be accomplished prior to the step of preparing. After the preparing and inserting are complete, the first length is unfolded so that it no longer overlies the second length, and the first length and the second length are contracted to the fully contracted state over the body.
The first length may be at a first end of the hollow tube, and the second length at a second end of the hollow tube. In another embodiment, there is a third length in the expanded state. The first length is at a first end of the hollow tube, and the third length is at a second end of the hollow tube, so that the second length is positioned between the first length and the third length. This configuration makes it easy to slip the third length of the folded hollow tube over the body.
Desirably, the materials properties of the hollow tube are such that a contraction ratio of an outer diameter of the hollow tube in the expanded state to an outer diameter of the hollow tube in the fully contracted state is from about 1.5:1 to about 2.5:1. The step of partially contracting preferably includes the step of contracting the hollow tube such that an outer diameter of the hollow tube in the partially contracted state is from about 5 to about 20 percent smaller than an outer diameter of the hollow tube in the expanded state.
The inner diameter of the partially contracted second length is reduced by at most only about 20 percent from the inner diameter of the expanded state. The folded configuration has a regular, circular inner diameter of the second length into which the body is easily inserted. The alternative embodiment with the fully expanded third length makes the insertion even easier. The body is inserted, but the shortened telescoped hollow tube is sufficiently shorter than the body such as the electrical cable so that the ends of the electrical cable are easily accessed for making connections. Once the work at the ends of the body is complete, the first length is folded back to its extended length to cover the entire length of the object. The entire hollow tube is then contracted to its fully contracted state.
Although the use of the shrinkable hollow tube is described in relation to its application to electrical cable, it may be used in other applications, such as to hold bundles of hydraulic tubing. It may also be used for decorative applications such as to apply a decorative ring to a cylindrical object.